The INMO says it's as a result of a recruitment stoppage by the HSE.
A nurse staffing crisis is forcing the closure of 12 beds at Tullamore hospital.
The Irish Nurses' and Midwives' Organisation says a recruitment "pause" from the HSE in April is now paralysing operations at the Midlands Regional Hospital.
There are currently 40 vacancies in Tullamore and Portlaoise hospitals respectively, with a further 60 in Mullingar.
The INMO's Midlands representative, Joe Hoolan, says it's a money-saving exercise from the health service that's only putting added pressure on front-line staff: